Population Genetics Flashcards
Only 10% of human DNA codes for genes, and only 1% are
Exons
The promoter upstream of the 5’ terminus regulates the initiation of DNA transcription into single stranded
mRNA
How many codons specify translation into the 20 amino acids of the protein?
64 (three are stop codons)
Non-corrected transcription errors make
Mutant (abnormal) proteins
Humans have 2 sets of homologous chromosomes (diploid). Thus, there are 2 copies of each
Gene (allele)
If both alleles are the same, the individual is said to be a
Homozygote
If the two alleles are different, the individual is a
Heterozygote
At a population level, there may be multiple alleles at each locus. These allelic variations can be expressed in different proportions in the
Population
A single nucleotide change (SNP) or insertion/deletion (Indel) of a nucleotide that has been transmitted throughout generations
Polymorphisms
Polymorphisms are a single nucleotide change (SNP) or insertion/deletion (Indel) of a nucleotide that has been transmitted throughout generations reaching a frequency of
1 in 100 in the population
The frequency of “Phenotypic Traits” caused by an allele within a loci can vary among
Populations
Remember that many phenotypic manifestations defy a simple Phenotype-Genotype Mendelian categorization and must be modeled using
Gene interactions together with environmental exposures
What are the assumptions needed for assuming we have a population in Hardy-Weinburg (H-W) equilibrium?
- ) Random mating
- ) No changes due to migration
- ) No large fluctuations in allele frequency (i.e. genetic drift)
- ) No positive or negative selection
Means that all genotypes reproduce equally well
No positive or negative selection
In H-W equilibrium, we can have no large fluctuations in allele frequency caused by the effects of: natural selection, genetic drift, founder effect, bottleneck, or
Inbreeding
Selection against homozygous individuals and advantage for heterozygotes in a given environment
Ex: the ability of sickle cell heterozygotes to fight off malaria
Natural selection
Variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
Genetic Drift
The frequency of Ellis-van Creveld syndrome in PA is greater than expected from random distribution of alleles, this is due to
Genetic drift
Characterized by short stature, polydactyly, and heart disease
Ellis-van Creveld syndrome
A deleterious rare allele seen at a relatively high frequency in a small/isolated population derived from 1 ancestor
Ex: Huntington’s Disease in Maracaibo
Founder effect
High frequency of an allele in a population that underwent historical population constrictions
-Ex: the frequency of Gaucher, Tay-Sachs, Torsion dystonia in the Ashkenazi Jewish population
Bottleneck effect
Consanguinous mating (between relatives) that increases the amount of homoxygotes
Inbreeding
Subpopulation stratification by selective mating (marriage arrangements) increases the rate of homozygotes and the probability of distinct phenotypic traits in some
Populations
Occurs in up to 60% of people in some geographic regions
Endogamy (marrying only within limits of tribe/community)
What leads to genetic variations among populations?
Natural selection, Genetic Drift, Founder effect, Bottleneck effect, and Inbreeding
Says that the chance that a genetic disorder will occur depends on the observed frequency of the disease in the population
Hardy-Weinberg principle